08/30/2017

Update: Portion size studies

See update from October 2018 below.

My textbook describes several studies from Dr. Brian Wansink's lab. They make excellent teaching examples because students are able to understand the theory and hypotheses almost immediately and therefore focus on the methodological details. For example, in Chapter 10 of the 2nd and 3rd editions, I feature studies in which pasta was served from either large or small serving bowls (van Kleef, Shimizu, & Wansink, 2012). And in the Supplemental Chapters on statistics, I feature a study involving stale and fresh popcorn serving sizes (Wansink & Kim, 2005).

Instructors and students should know that Wansink's lab has come under intense scrutiny over the past year. First, he was attacked for publishing a (seemingly innocent) blog post admitting to questionable research practices (including HARKing--see Chapter 14 of the 3rd edition). Second, some researchers have alleged impossible values in data tables which suggest some sloppy statistical reporting. Third, he has admitted to using the same wording in more than one publication (sometimes called self-plagiarizing) and publishing some of his data in two places. According to reports, Wansink appears open to checking all past work and publishing corrections as needed. This story in The Chronicle summarizes the issues in a fairly balanced report (from March, 2017), and this story explains the results of an inquiry by Wansink's institution, Cornell University (from April, 2017).

In two of my own classes, I conducted demonstration versions of portion size studies, and I have obtained the predicted pattern, with large effect sizes, both times. In my opinion, the portion size effect is real. However, it's definitely worth telling students about the alleged problems with Wansink's work.

So far, the study in Chapter 10 (van Kleef et al., 2012) has not been identified as problematic. However, the popcorn study (Wansink & Kim, 2005) was alleged to have reported impossible values on a key table; the problems were described as "relatively minor" (Source). I changed that table for Figure S1.7 of the 3rd Edition in order to delete the ANOVA values that were found to be problematic. The entire table and discussion will be omitted from the 4th edition. However, despite my changes to the table, I think instructors should use Figure S1.7 only as an example for how to read data tables, and not endorse it as a replicable scientific finding.

Dr. Wansink has agreed to resign from Cornell University after six of his articles were retracted from the journal JAMA and after his university concluded that he had engaged in academic misconduct. Here's a CNN story on the situation.

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